A process for preparing cumene by reacting benzene with propylene, a process for preparing cumene hydroperoxide by oxidizing cumene and a process for preparing phenol and acetone by acid decomposing cumene hydroperoxide are publicly known, and a process combining these reactions is a phenol preparation process generally called a cumene process. At present, this cumene process is the mainstream of the phenol preparation process.
This cumene process is characterized in that acetone is simultaneously produced, and this is advantageous when acetone is needed at the same time, but this is economically disadvantageous when acetone is in excess. Then, in order to lead a difference in price between an olefin as a raw material and a ketone produced simultaneously to an advantageous direction, there has been proposed, for example, a process in which secondary butylbenzene obtained from n-butene and benzene is oxidized and acid decomposed to obtain phenol and methyl ethyl ketone at the same time (see patent document 1 and patent document 2). In this process, however, the selectivity of the aimed secondary butylbenzene hydroperoxide obtained by the oxidation of secondary butylbenzene is only about 80%, and in addition, not less than 15% of acetophenone is formed as a side product. Therefore, this process is inferior, as the phenol preparation process, to the cumene process in yield.
Further, there has been also proposed a process in which cyclohexylbenzene obtained from cyclohexene and benzene is oxidized and acid decomposed to obtain phenol and cyclohexanone. In this process, phenol is obtained by dehydrogenating the resulting cyclohexanone, so that formation of a ketone as a side product can be avoided formally. In this process, however, the yield of the aimed cyclohexylbenzene hydroperoxide obtained by the oxidation reaction of cyclobenzene is much lower, and its industrial value is low.
Accordingly, in order to avoid problems of propylene that is a raw material and acetone that is produced simultaneously while maintaining an advantage of the cumene process wherein the yields of oxidation and acid decomposition are highest, there have been proposed processes in which acetone simultaneously produced is recycled as a raw material of the cumene process by the use of various methods. Acetone can be readily converted into isopropanol by hydrogenation, so that a process in which isopropanol is further subjected to dehydration reaction to convert it into propylene, then the propylene is reacted with benzene to obtain cumene and the propylene is recycled as a raw material of the cumene process has been proposed (see patent document 3). In this process, however, there is a problem that the two steps, i.e., a hydrogenation step and a dehydration step are further required.
Accordingly, a process in which isopropanol obtained by hydrogenation of acetone is directly reacted with benzene to obtain cumene has been proposed (see patent document 4 and patent document 5). Especially in a patent document 6, there has been described a process in which acetone simultaneously produced is converted into isopropanol, then the isopropanol is reacted with benzene to obtain cumene, and using the cumene, phenol is prepared. In this process, however, a hydrogenation step is required in addition to the original cumene process.
In contrast with the above, as a process in which acetone simultaneously produced is recycled without increasing the number of steps of the conventional cumene process, that is, a process in which acetone is directly reacted with benzene, there has been disclosed a process for preparing an alkylated aromatic compound, comprising reacting an aromatic compound with a ketone and hydrogen in the presence of a solid acid substance and a catalyst composition containing copper (see patent document 7). As the Cu-based reduction catalyst in the examples, however, a Cu-based catalyst containing, as a second component, Cr or Al and a slight amount of Zn is only disclosed. Further, it is described that zeolite can be used as the solid acid substance, but β-zeolite is only disclosed in the examples. The present inventors used the copper-chromium catalyst in the examples and chabazite as the solid acid substance, but cumene was not formed virtually. Moreover, among zeolites, there is one having much smaller pore diameters as compared with molecular diameters of benzene or cumene (non-patent document 1), so that it is readily presumed that the reaction itself is impossible with such a catalyst. As described above, formation of cumene is not satisfactory in the case of a solid acid substance different from the examples. As a result of actual inspection by the present inventors, a hydrocarbon derived from acetone is formed as a side product by any of the above catalysts, and the processes proved to be unsatisfactory as industrial production processes. That is to say, the selectivity of cumene is extremely low in the case of the conventional catalysts, and the industrial level has not been reached at all.
Patent document 1: Japanese Patent Laid-Open Publication No. 91972/1982
Patent document 2: U.S. Pre Grant Patent No. 0162448/2004
Patent document 3: Japanese Patent Laid-Open Publication No. 174737/1990
Patent document 4: Japanese Patent Laid-Open Publication No. 231442/1990
Patent document 5: Japanese Patent Laid-Open Publication No. 35497/1999
Patent document 6: National Publication of International Patent No. 523985/2003
Patent document 7: National Publication of International Patent No. 513116/2005
Non-patent document 1: ZEOLITES, Vol. 4, pp. 202-213, 1984